For some reason (probably permissions), ALL .itb files are returning 403. I am about to go out for few hours - I'll check on it later today unless someone else fixes it.
I corrected the perms on the files affected however, I think the build system staging of these files needs to be examined to see if it can be prevented. I have not looked at the build system in quite a while so I need to spend some time with it in order to find the cause of the problem. It would be nice if @jow would look into this when he returns from vacation.
I located the root cause of this problem. It is in the u-boot mkimage utility - it creates the file with 0700 perms. I have a patch to fix the problem which I'll push to our source repo in a bit.